[147989] in North American Network Operators' Group
Re: IPTV and ASM
daemon@ATHENA.MIT.EDU (Mark Tinka)
Thu Dec 29 04:44:08 2011
From: Mark Tinka <mtinka@globaltransit.net>
To: nanog@nanog.org
Date: Thu, 29 Dec 2011 17:42:02 +0800
In-Reply-To: <FBA571D6-241E-4B4D-AF61-806B7576227D@ericsson.com>
Reply-To: mtinka@globaltransit.net
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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On Thursday, December 29, 2011 07:32:38 AM Jeff Tantsura=20
wrote:
> To my knowledge in most today's networks even if legacy
> equipment don't support IGMPv3 most likely 1st hop
> router does static translation and SSM upstream.
Yes, SSM Mapping allows for PIM-SSM to be used in a network=20
where the receivers don't support IGMPv3. But it tends to be=20
static in nature, although both Juniper and Cisco suggest=20
that dynamically-configured options are possible.
I couldn't quite decode the Juniper dynamic method, but the=20
Cisco one appears to be based on DNS. That should be=20
interesting (and a colossal screw-up if things are poorly=20
maintained):
http://www.cisco.com/en/US/docs/ios/12_3t/12_3t2/feature/guide/gtssmma.html=
#wp1119180
> The
> reason not to migrate to SSM is usually - ASM is already
> there and works just fine :)
This is our case.
> Cost to support RP
> infrastructure is usually the main non-technical factor
> to not to use ASM. Would be interested to hear from the
> SPs on the list.
=46or us, the cost of the RP isn't an issue. The Sender PE=20
routers (in NG-MVPN speak, the ISP's routers that are=20
connected toward the Source) are also the RP's.
But due to the use of NG-MVPN, and how we designed our=20
Multicast backbone, there really isn't any need for the=20
Receiver PE routers to contact the RP whenever a customer is=20
joining a group.
BGP has been extended to handle PIM messages in NG-MVPN.=20
When a Source is discovered by the Sender PE router, it=20
generates a Type 5 SA-AD (Source Active, Auto-discovery) =20
BGP update route which is sent to all Receiver PE routers=20
participating in the MVPN. This Type 5 route is generated=20
from the PIM Register state that is created by PIM running=20
between the Sender PE and CE routers.
If the Receiver PE router is configured to operate the MVPN=20
in the SPT-only mode, it generates a Type 7 (C-S,C-G) route=20
for every Type 5 route it received, effectively creating the=20
necessary state in the local Receiver PE router. Once=20
customers send (*,G) IGMP reports requesting to join=20
Multicast groups, that state is already present on the=20
Receiver PE router, and traffic starts flowing immediately=20
downstream.
If the Receiver PE router is configured to operate the MVPN=20
in RPT-SPT mode, it will follow regular PIM mecahnisms when=20
users are trying to join groups, i.e., Join messages are=20
forwarded toward the RP along the RPT, and then Multicast=20
traffic forwarded along the SPT once the correct (C-S,C-G)=20
state is created locally.
The above explanation is somewhat simplified, but represents=20
the general architecture of how things work in NG-MVPN's.
=46or us, SPT-only mode makes sense because we have IPTv=20
probes attached to all Receiver PE routers; and since=20
they're collecting telemetry for all IPTv channels, no point=20
running the RPT-SPT mode.
Please note that this whole setup doesn't require MSDP,=20
which is nice!
Cheers,
Mark.
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